Flexible polymeric films are widely used as packaging materials for a vast range of goods.
Furthermore, a variety of synthetic polymers are used for producing such packaging materials, for example films made from synthetic polymers, such as (polyolefins [e.g. polyethylene and/or, polypropylene] polystyrene and/or polyesters) and/or natural polymers (such as cellulosic materials and/or biopolymers e.g. polylactic acid).
One particular packaging use for such films is as an overwrap for a variety of goods, for example for cigarette packets, video tapes, cookies etc., the films being sealed tightly over the goods. However, the very properties which confer desirable properties on the films as packaging materials, for example high strength and tear resistance, make such packages difficult to open because the films of which they are made are difficult to tear.
In order to facilitate the opening of such packages, so-called “tear tapes” have been provided which consist of a narrow strip of a polymeric film adhered to internal surface of the packaging film, a tab of the tear tape being left free on the outside of package to facilitate its opening. The package can then be opened by pulling the tear tape through the packaging film.
As an alternative to tear tapes, it is also known to use “tear strips” in a film. Tear strips differ to tear tapes in that a tear strip is integral to the film itself, rather than a separate film located adjacent the packaging film. A tear strip is typically defined by two parallel lines of weakness in a film, so that when the tear strip is pulled in a direction generally away from the rest of the packaging the lines of weakness break in a controlled manner and the packaging can be opened.
US2005087282 describes a non-invasive tear mechanism for a flexible packaging, the non-invasive tear mechanism comprises a horn side wall and an anvil side wall joined to the horn side wall. A plurality of junctions are formed in flexible packaging and form a line of weakness in the flexible packaging. The plurality of junctions that form the line of weakness allows the flexible packaging to be manually opened, and the junctions are non-invasive in that the flexible packaging is not cut or scored when the non-invasive tear mechanism is formed.
GB 458375 discloses an arrangement where a wrapping blank is used which has a box pleat provided along the whole length of the blank. The wrapper is folded in to a U-shape about the article to be enclosed and the side folds of the wrapper are then formed and secured. The end of the package is closed by end folds and end flaps. The outer end fold has slits formed adjacent to the pleat and the package can be opened by initiating tearing at the slits so that the tear propagates along each side of the pleat.
U.S. Pat. No. 6,120,629 relates to ultrasonically processing a web to produce discrete treated regions, comprising elongated bands, across the width of the web, e.g., for use as tear lines in a continuous tape web.
GB-A-2311752 discloses a semi-matt plastics film having a regular embossed pattern which, when rubbed against itself, emits a distinctive noise.
US-A-2007/0104917 discloses a multiple layer material construction with a break line formed by a line-shaped, successive arrangement of blind holes separated by webs, there being abrupt jumps in material thickness along the break line such that a noise is generated when the break line tears.
EP-A-0343857 discloses and outer wrapper for a container which opens along an oblique parting line, the wrapper including a tear tape having a pattern such that each portion of the parting line has an aligned tear tape portion.
EP-A-1666376 discloses a tear tape and a weakening line next to the tear tape, the longitudinal axis of the weakening line being substantially perpendicular to the tear tape.
One problem identified in the film packaging market is how to make packaging more distinctive and preferably easier and more enjoyable to use. There are several commonly used film treatment techniques which can advantageously improve the tactile properties of a film, or part of a film. There are also known methods of treating regions of a film to change the light reflecting/absorbing properties, both externally and internally of the film to enhance the films aesthetic properties.
The known techniques for modifying the distinctive properties of a film are, in general, limited to its tactile and aesthetic features. However, in a film having a tear tape it has been found that it is advantageously possible to deliberately use the mechanical energy from the tearing process to create acoustic energy
US 2007/104917 is directed to packaging comprising a multiple-layer material construction with a break line which is formed by a line-shaped, successive arrangement of blind holes separated by webs and in which the multiple-layer material construction comprises at least one layer which absorbs laser radiation and a layer which reflects this laser radiation. A radiation-absorbing layer forms the surface layer of the packaging, and the blind holes of the surface layer extend into the packaging until the reflecting layer, and the web widths are substantially constant over the depths of the blind holes so that there are abrupt jumps in material thickness along the break line, and a clearly audible noise is generated when these jumps in material thickness are overcome when the break line tears.